Wireless communication system and wireless base station

ABSTRACT

A wireless communication system including: a wireless terminal, and a wireless base station configured to: perform a wireless communication with the wireless terminal, and perform at least a specified processing included in a baseband processing for the wireless communication, the baseband processing being shared between the wireless base station and a different wireless base station, the specified processing being a processing that has a limitation of processing time.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of theprior Japanese Patent Application No. 2014-254834, filed on Dec. 17,2014, the entire contents of which are incorporated herein by reference.

FIELD

The embodiments discussed herein are related to a wireless communicationsystem, a wireless base station, a baseband unit, a control device, anda wireless communication method.

BACKGROUND

Cellular wireless communication systems based on wireless communicationprotocols, such as wideband code division multiple access (W-CDMA), longterm evolution (LTE), and the like, have been widely used. A cellularwireless communication system includes many wireless base stationsforming many cells. Therefore, in recent years, a large number ofwireless base stations have been disposed all around.

If a sufficient number of wireless base stations are not disposed, cellsare not formed in a wide range, and a problem arises in which a cellularservice area (a cover area) may be limited. As a matter of course, itimposes large cost to dispose a wireless base station. Therefore,techniques for efficiently forming a cell have been great concerns ofservice providers (wireless communication carriers) in recent years.

Incidentally, in general, a wireless base station includes a basebandunit (BBU) and a radio frequency unit (an RF unit). The BBU performsbaseband processing that is processing performed on a baseband signal.In contrast, the RF unit mutually converts a baseband signal and an RFsignal from one to another and performs transmission and reception of anRF signal via an antenna. In this case, a baseband signal is a lowfrequency digital signal. Since there is a limit in performing complexprocessing on an RF signal that is a radio frequency analog signal, atreception of an RF signal, a wireless base station demodulates the RFsignal received via the antenna to a baseband, and then, performsvarious types of processing thereon. At transmission of an RF signal,the wireless base station performs various types of processing on abaseband signal related to information that is desired to betransmitted, modulates the baseband signal to an RF signal, and then,transmits the RF signal via the antenna.

As described above, in general, a cellular wireless base station forms acell. In a known cellular wireless communication system, a singlewireless base station forms a single cell. Specifically, a knownwireless base station has a configuration in which a single BBU and asingle RF unit are integrated as one unit and thus is enabled to form asingle cell.

In contrast, a configuration in which a single wireless base stationforms a plurality of cells was recently introduced. Such a wireless basestation includes a single BBU and a plurality of RF units. The BBU andthe RF units are physically separated from one another, and are coupledto one another via an optical fiber or the like. Thus, a single wirelessbase station is allowed to form a plurality of cells (cells of a numbercorresponding to the number of RF units).

Thus, a configuration in which a BBU is not provided for each cell isallowed, and therefore, a computer resource per cell that is to beprepared in a BBU may be reduced (due to a statistical multiplexingeffect). Furthermore, an increase in efficiency of a computer resourcein an entire system is allowed.

Note that there are cases where such a configuration as one describedabove, in which a plurality of RF units is controlled by a single BBU,is called centralized radio access network (C-RAN). Also, there arecases where a BBU in a wireless base station having a C-RANconfiguration is specifically called centralized baseband unit (CBBU).Furthermore, there are cases where a device in a wireless base stationhaving a C-RAN configuration, which corresponds to an RF unit, is calleda remote radio unit (RRU) or a remote radio head (RRH).

Japanese Laid-open Patent Publication No. 2010-213007, JapaneseLaid-open Patent Publication No. 2012-182792, Japanese NationalPublication of International Patent Application No. 2014-514848, andJapanese Laid-open Patent Publication No. 2007-228213 discuss relatedart.

SUMMARY

According to an aspect of the invention, a wireless communication systemincluding: a wireless terminal, and a wireless base station configuredto: perform a wireless communication with the wireless terminal, andperform at least a specified processing included in a basebandprocessing for the wireless communication, the baseband processing beingshared between the wireless base station and a different wireless basestation, the specified processing being a processing that has alimitation of processing time.

The object and advantages of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a first embodiment;

FIG. 2A and FIG. 2B are diagrams illustrating protocol stacks of LTE;

FIG. 3 is a diagram illustrating a system configuration according to asecond embodiment;

FIG. 4 is a sequence diagram illustrating a flow of processing accordingto the second embodiment;

FIG. 5 is a diagram illustrating a system configuration according to athird embodiment;

FIG. 6 is a sequence diagram illustrating a flow of processing accordingto the third embodiment;

FIG. 7 is a diagram illustrating an example of a functionalconfiguration of a wireless base station in each embodiment;

FIG. 8 is a diagram illustrating an example of a functionalconfiguration of a control device in the third embodiment;

FIG. 9 is a diagram illustrating a hardware configuration of a wirelessbase station in each embodiment; and

FIG. 10 is a diagram illustrating an example of a hardware configurationof the control device in the third embodiment.

DESCRIPTION OF EMBODIMENTS

Baseband processing performed by a BBU includes a large number ofindividual processes and, among the processes, there is a process whichhas a time limitation (a time restraint) defined by a specification of awireless communication protocol. For example, in the specification(standard specification) of LTE, it is defined that, in a functioncalled hybrid automatic repeat request (HARQ), when a wireless basestation receives uplink data from a wireless terminal, the wireless basestation sends an ACK signal or a NACK signal as a response in a subframefour subframes after a subframe of the uplink data (in the case of FDD).Such a time limitation in the specification is desired to be strictlysatisfied, and therefore, it is desired that the BBU performs basebandprocessing such that the time limitation is satisfied. Specifically, theBBU finishes demodulation and decoding of the received uplink data,determines whether or not reception was successfully performed, andprepares for sending the ACK signal or the NACK signal as a response ina little over three subframes (corresponding to a little over threemilliseconds).

However, the load of the BBU is increased by managing a plurality ofcells, and thus, reduction in performance is caused in the BBU. As aresult, there might be cases where the BBU does not satisfy the timelimitation defined by the specification.

Furthermore, in a C-RAN configuration, a propagation delay between a BBU(CBBU) and an RRU occurs for constructive reasons. Therefore, a morestrict time limitation is imposed on the BBU.

This problem may be solved to a certain extent by introducing ahigh-speed hardware to a BBU, but there are cases where introduction ofa high-speed hardware is difficult because such a hardware is veryexpensive.

In view of the foregoing, a technique disclosed herein has been devised,and it is therefore an object of the present disclosure to provide awireless communication system, a wireless base station, a baseband unit,a control device, and a wireless communication method which enablecompliance with a time limitation defined by the specification, evenwhen an overload or the like occurs in a BBU that manages a plurality ofcells.

Embodiments of disclosed wireless communication system, wireless basestation, baseband unit, control device, and wireless communicationmethod will be described below with reference to the accompanyingdrawings. Note that, for the sake of convenience, each of theembodiments will be separately described, but it is needless to say thatthe embodiments may be combined to achieve advantages of the combinationand furthermore to increase utility.

Note that, in the present disclosure, for example, when a member isdenoted by a wireless base station 1, there are a case where thewireless base station 1 indicates an individual wireless base stationand a case where the wireless base station 1 indicates an assembly ofwireless base stations, and it is desired to determine, as appropriate,which the former case or the latter case applies to the description,depending on context.

First Embodiment

A first embodiment will be described with reference to FIG. 1. Asillustrated in FIG. 1, a wireless communication system according to thefirst embodiment includes a first wireless base station 1#1 configuredto perform wireless communication with a wireless terminal 2 and one ormore other wireless base stations 1, and, in performing the wirelesscommunication, baseband processing performed for the wirelesscommunication is shared between the first wireless base station 1#1 anda second wireless base station 1#2, which is one of the one or moreother wireless base stations 1, and the first wireless base station 1#1performs at least a specific process, in the baseband processing, whichhas a processing time limitation.

A technical significance of the first embodiment will be described. Asdescribed above, the present disclosure focuses on a problem in which,when the load of baseband processing of the wireless base station 1 ishigh, or in like case, a time limitation for baseband processing basedon a specification of a wireless communication protocol is notsatisfied.

Thus, a case where the load of baseband processing of one of thewireless base stations 1 (which will be referred to as a first wirelessbase station 1#1 for the sake of convenience) is high will beconsidered. In this case, in the wireless communication system accordingto the first embodiment, baseband processing of the wireless basestation 1 is shared with one of the one or more other wireless basestations 1 (which will be referred to as the second wireless basestation 1#2 for the sake of convenience). That is, a part of thebaseband processing of the one of the wireless base stations 1 is takenover by the one of the one or more other wireless base stations 1. Thus,the load of the baseband processing of the one of the wireless basestations 1 is dispersed, and the load of the one of the wireless basestations 1 is reduced.

However, only with the foregoing consideration, there is still aprobability that the above-described problem is not solved. Whenbaseband processing is shared among the plurality of wireless basestations 1, a baseband signal is passed among the plurality of wirelessbase stations 1. Passing a baseband signal naturally causes apropagation delay and, in general, a distance between BBUs is longerthan a distance between a BBU and an RRU. Therefore, a propagation delaycaused by passing a baseband signal is relatively large.

Therefore, when baseband processing is randomly shared, although theload of the wireless base station 1, which is a share source, isreduced, a relatively large propagation delay is added, so that anentire processing time of the baseband processing might be increased. Insuch a case, the above-described problem of a time limitation forbaseband processing based on the specification of a wirelesscommunication protocol is not solved.

Thus, in a wireless communication system according to the firstembodiment, when baseband processing of one of the wireless basestations 1 is shared with one of the one or more other wireless basestations 1, a process, in the baseband processing, which has a timelimitation, is performed by the one of the wireless base stations 1 (byitself). A process, in the baseband processing, which does not have atime limitation, is taken over by one of the one or more other wirelessbase stations 1. In this case, processing is divided depending on theexistence or non-existence of a time limitation, but note that theexistence or non-existence of a time limitation may be interpreted aswhether or not there is a time limitation, and also, may be interpretedas whether relatively large or small (or whether relatively strict orloose) a time limitation is.

Note that, in the background of the present disclosure and the problemsto be solved by the present disclosure, which have been described above,discussions were made based on a wireless communication system includinga wireless base station 1 having a so-called C-RAN configuration inwhich a BBU and an RRU are physically separated. However, note that thepresent disclosure is not limited to such a wireless communicationsystem, but may be applied to a wireless communication system includinga wireless base station 1 of a known (integrated) type and a wirelessbase station 1 having a C-RAN configuration together and a wirelesscommunication system including a wireless base station 1 of a known typeonly. To be brief, the problem to be solved by the present disclosure ismerely remarkable in a wireless base station 1 having a C-RANconfiguration, and a wireless base station 1 having a C-RANconfiguration is not the premise of the present disclosure.

To summarize the foregoing, in the first embodiment, even when basebandprocessing of the wireless base station 1#1 is shared with the secondwireless base station 1#2, which is one of the one or more otherwireless base stations 1, the first wireless base station 1#1 performs(by itself) at least a process, in the baseband processing, which has atime limitation. Thus, the process, in the baseband processing, whichhas a time limitation, is not influenced by a delay caused by passing ofa baseband signal. Therefore, according to the first embodiment, theabove-described problem of a time limitation for baseband processingbased on the specification of a wireless communication protocol may besolved.

Second Embodiment

A second embodiment will be described below with reference to FIG. 2 toFIG. 4. The second embodiment corresponds to a case where the presentdisclosure is applied to a wireless communication system based on LTE.However, note that application of the present disclosure is not limitedto LTE and the present disclosure is applicable to a wirelesscommunication system based on another wireless communication protocol ina similar manner.

In the second embodiment, similar to the first embodiment, when basebandprocessing of one of the wireless base stations 1 is shared with one ofthe one or more other wireless base stations 1, the one of the wirelessbase stations 1 performs (by itself) a process, in the basebandprocessing, which has a time limitation. A process, in the basebandprocessing, which does not have a time limitation, may be taken over bythe one of the one or more other wireless base stations 1.

In the present disclosure, a key point is that how “a process which hasa time limitation” and “a process which does not have a time limitation”in baseband processing are divided. In the second embodiment, thedivision between these processes is performed based on a protocol stackof LTE. This point will be described first below.

First, the protocol stack of LTE will be described with reference toFIG. 2A and FIG. 2B. FIG. 2A is a diagram illustrating a protocol stackof a user plane that is a protocol used for transferring user data inLTE. FIG. 2B is a diagram illustrating a protocol stack of a controlplane that is a protocol used for transferring a control signal in LTE.These protocol stacks are defined by the standard specification of LTE.Therefore, every baseband processing in an LTE system is performed inaccordance with these protocol stacks.

The protocol stack of a user plane of LTE illustrated in FIG. 2Aincludes a physical layer, a medium access control sublayer (a MAClayer), a radio link control sublayer (a RLC layer), and a packet dataconvergence protocol sublayer (a PDCP layer) stacked from the bottom.The physical layer is a hierarchical layer corresponding to a firstlayer (Layer 1) in an open system interconnection (OSI) reference model,and handles many processes in order to realize information transmissionwith a wireless signal that is a physical medium. The MAC layer, the RLClayer, and the PDCP layer, on the other hand, are layers correspondingto a second layer (Layer 2) in the OSI reference model. The MAC layerhandles multiple separation of a transmission and reception signal, andthe like, the RLC layer handles retransmission control, and the like,and the PDCP layer handles a security function, and the like.

The protocol stack of a control plane of LTE illustrated in FIG. 2Bincludes a radio access control sublayer (an RRC layer) above thephysical layer, the MAC layer, the RLC layer, and the PDCP layer, whichhave been described above. The RRC layer is a layer corresponding to athird layer (Layer 3) in the OSI reference model and handles manyprocesses related to control of a wireless link.

Thus, a wireless communication protocol of LTE has a hierarchicalprotocol stack. Therefore, baseband processing performed by a BBU 11corresponds to the protocol stack and hierarchical processing isperformed.

Incidentally, like demodulation and decoding processing and the like inaccordance with the HARQ, which has been described above, there is aprocess for which a strict time limitation is defined in the (standard)specification of LTE. Needless to say, such an individual timelimitation is eventually defined by a specification. However, in view ofthe above-described protocol stacks, tendencies of such time limitationsmay be found to a certain extent.

Specifically, there is a tendency that the lower a hierarchical layer ina protocol stack is, the more strict a time limitation is relatively. Incontrast, there is a tendency that the higher a hierarchical layer in aprotocol stack is, the looser a time imitation is relatively. As aspecific example, for a process, such as demodulation and decoding andthe like, in accordance with the above-described HARQ, a strict timelimitation is defined in the specification, and the processing isexecuted in the physical layer, which is the lowest layer, (HARQ controlis performed by the MAC layer).

As described above, an individual time limitation is eventually definedby the specification but, in general, depending on the level of ahierarchical layer in a protocol stack, the strictness of a timelimitation on a process performed by the hierarchical layer differs.This difference occurs because a process of a hierarchical layer ispremised on a process of a lower hierarchical layer, and is consideredto be fateful in a wireless communication protocol having a hierarchicalprotocol stack.

In the view of the foregoing, in the second embodiment, hierarchicallayers forming a protocol stack of LTE are divided into two, among thehierarchical layers, a relatively low hierarchical layer is handled as ahierarchical layer which performs “a process that has a timelimitation”, and a relatively high hierarchical layer is handled as ahierarchical layer which performs “a process that does not have a timelimitation”. More specifically, as an example, the physical layer ishandled as a hierarchical layer that performs “a process that has a timelimitation”, and the MAC layer and higher layers are handled ashierarchical layers each of which performs “a process that does not havea time restriction”. Thus, for example, a process, such as demodulationand decoding, and the like, in accordance with the HARQ, which has beendescribed above, is categorized as “a process that has a timelimitation”.

In the second embodiment, based on the above-described division,baseband processing is shared among the wireless base stations 1. Thatis, when the baseband processing of one of the wireless base stations 1is shared with one of the one or more other wireless base stations 1, aprocess of the physical layer (which corresponds to the relatively lowhierarchical layer) in the baseband processing is performed by the oneof the wireless base stations 1 (by itself). Processes of the MAC layerand higher layers (each of which corresponds to the relatively highhierarchical layer) in the baseband processing may be taken over by theone of the one or more other wireless base stations 1. This is a keypoint of the second embodiment.

Next, a system configuration of a wireless communication systemaccording to the second embodiment will be described with reference toFIG. 3. As a premise, the wireless communication system according to thesecond embodiment includes a plurality of wireless base stations 1. InFIG. 3, as an example, the wireless communication system includes threewireless base stations 1. Each of the wireless base stations 1 includesone BBU 11 and, for example, three RRUs 12. Thus, each of the wirelessbase stations 1 illustrated in FIG. 3 forms and controls three cells 1C.

In FIG. 3, the BBUs 11 are coupled to one another by an optical fiber orthe like via an optical switch (not illustrated) or the like, and mayperform low-delay communication. Also, each of the BBUs 11 and thecorresponding one of the RRUs 12 are coupled to each other by an opticalfiber or the like via an optical switch (not illustrated) or the like,and may perform low-delay communication. However, note that theconfiguration illustrated in FIG. 3 is an example and the presentdisclosure may be implemented without being limited to the configurationwithout departing from the gist of the present disclosure.

As illustrated also in FIG. 3, for the sake of convenience, the threewireless base stations 1 are referred to as a first wireless basestation 1#1, a second wireless base station 1#2, and a third wirelessbase station 1#3. The respective BBUs 11 of the first to third wirelessbase stations 1#1, 1#2, and 1#3 are referred to as a first BBU 11#1, asecond BBU 11#2, and a third BBU 11#3. Furthermore, for example, thethree RRUs 12 of the first wireless base station 1#1 are referred to asa first RRU 12 a#1 of the first wireless base station 1#1, an RRU 12 b#1of the first wireless base station 1#1, and an RRU 12 c#1 of the firstwireless base station 1#1, and the cells 1C formed by them are referredto as a first cell 1Ca#1 of the first wireless base station 1#1, asecond cell 1Cb#1 of the first wireless base station 1#1, and a thirdcell 1Cc#1 of the first wireless base station 1#1. The RRUs 12 of thesecond wireless base station 1#2 and the third wireless base station1#3, and the cells 1Cs formed by them are similarly referred.

Next, a sequence diagram illustrating a flow of processing performed ina wireless communication system according to the second embodiment withreference to FIG. 4.

FIG. 4 illustrates a flow of processing performed when each ofprocessing loads of the wireless base stations 1 is used as an indexthat is considered in determining whether or not sharing of basebandprocessing is desired and selecting one of the wireless base stations 1,which is a share destination of baseband processing. However, note thatthe processing loads of the wireless base stations 1 are merely anexample of the index, and another element may be considered. This pointwill be occasionally described in detail.

FIG. 4 illustrates, as an example, a processing sequence when the firstwireless base station 1#1 shares baseband processing with the secondwireless base station 1#2 and the third wireless base station 1#3, whichcorrespond to the one or more other wireless base stations 1. In otherwords, FIG. 4 illustrates a processing sequence when the first wirelessbase station 1#1 is a share source of baseband processing and the one ormore other wireless base stations 1 are share destinations of thebaseband processing. However, for each of cases where the secondwireless base station 1#2 is a share source of baseband processing andwhere the third wireless base station 1#3 is a share source of basebandprocessing, although the description thereof will be omitted herein, itis needless to say that similar processing may be performed. Forexample, when the second wireless base station 1#2 is a share source ofbaseband processing, baseband destinations are the first wireless basestation 1#1 and the third wireless base station 1#3.

Processing of FIG. 4 will be sequentially described. First, in S101,each of the wireless base stations 1 (the first wireless base station1#1 to the third wireless base station 1#3) acquires information (anindex) related to the processing load of the wireless base station 1itself. Acquisition of information related to the processing load may beregularly performed and may be performed in response to a predeterminedtrigger.

As information related to the processing load acquired in S101,arbitrary information may be used. For example, each of the wirelessbase stations 1 may use, as information related to the processing load,the number of wireless terminals 2 managed by the wireless base station1 itself. “The wireless terminals 2 managed by the wireless base station1 itself” herein may be described, in other words, as wireless terminals2 each of which is coupled to the corresponding one of cells (that is,the cells C1 formed by the RRUs 12 under control of the wireless basestation 1 itself) formed by the wireless base station 1 itself. Thenumber of the wireless terminals 2 is directly linked to the magnitudeof the processing load of the wireless base station 1, and therefore, isconsidered preferable as information related to the processing load.

Each of the wireless base stations 1 may use, as information related tothe processing load, a monitoring result for a computer resource of thewireless base station 1 itself. Examples of the computer resource thatis to be monitored include the use rate of a processor, such as a DSP, aCPU, and the like, which is mounted therein, the user rate of a memory,such as a RAM, and the like. Furthermore, each of the wireless basestations 1 may also use a wireless resource usage, a data processingamount, a power consumption, an inside temperature, and the like. In anycase, each of the wireless base stations 1 acquires information relatedto the processing load of the wireless base station 1 itself in S101.

In S102 of FIG. 4, each of the wireless base stations 1 (the firstwireless base station 1#1 to the third wireless base station 1#3)exchanges information related to the processing load of the wirelessbase station 1 itself acquired in S101 with the other ones of thewireless base stations 1. The exchange of information related to theprocessing load in S102 may be performed in an arbitrary method. Forexample, each of the wireless base stations 1 may spontaneously transmitinformation to the other ones of the wireless base stations 1 atpredetermined timings, and may transmit information in response to arequest from each of the other ones of the wireless base stations 1.

Through the information exchange of S102, the first wireless basestation 1#1 may acquire information related to the processing load ofeach of the second wireless base station 1#2 and the third wireless basestation 1#3.

In S103 of FIG. 4, the first wireless base station 1#1 determineswhether or not sharing of baseband processing is desired. In this case,the first wireless base station 1#1 determines whether or not sharing ofbaseband processing is desired, based on information related to theprocessing load of the first wireless base station 1#1 itself acquiredin S101. If the processing load of the first wireless base station 1#1is sufficiently small, it is not highly desired that the basebandprocessing is shared with the one or more other wireless base stations1. Therefore, it is considered reasonable to consider a self processingload in determining whether or not sharing of baseband processing isdesired.

For example, in S103, the first wireless base station 1#1 may determinewhether or not sharing of baseband processing is desired, based on thenumber of wireless terminals 2 managed by the first wireless basestation 1#1 itself, which has been acquired in S101. Specifically, ifthe number of wireless terminals 2 managed by the first wireless basestation 1#1 itself is a predetermined number or more, the first wirelessbase station 1#1 determines that the sharing of baseband processing isdesired, and if the number of wireless terminals 2 managed by the firstwireless base station 1#1 itself is less than the predetermined number,the first wireless base station 1#1 determines that the sharing ofbaseband processing is not desired.

In S103 of FIG. 4, as an example, assume that the first wireless basestation 1#1 determines that sharing of baseband processing is desired.

In S104 of FIG. 4, the first wireless base station 1#1 determines nextprocessing, based on a determination result of S103. Specifically, if itis determined in S103 that sharing of baseband processing is desired,the first wireless base station 1#1 causes the process to proceed to theprocessing in S105. On the other hand, if it is determined in S103 thatsharing of baseband processing is not desired, the first wireless basestation 1#1 causes the process to return to the processing in S101. Thatis, as long as it is determined in S103 that sharing of basebandprocessing is not desired, the determination of S101 to S103 isrepeated.

As described above, if it is determined in S103 of FIG. 4 that sharingof baseband processing is desired, the first wireless base station #1causes the process to proceed to the processing in S105. In this case,in S105, the first wireless base station 1#1 selects (determines) one ofthe one ore other wireless base stations 1, which is to be sharedestinations of baseband processing. That is, in S105, the firstwireless base station 1#1 selects, when baseband processing performed bythe first wireless base station 1#1 is shared with one of the one ormore other wireless base stations 1, one of the one or more otherwireless base stations 1. Note that, in the first embodiment, the secondwireless base station 1#2 and the third wireless base station 1#3correspond to the one or more other wireless base stations 1.

In this case, the first wireless base station 1#1 selects, based oninformation related to the processing loads of the one or more otherwireless base stations 1 acquired in S102, a share destination of thebaseband processing. If the processing loads of the one or more otherwireless base stations 1 are not considered, a case might arise in whichone of the one or more other wireless base stations 1 the load of whichis already sufficiently high is selected as a share destination ofbaseband processing. In such a case, there is a probability that, aftertaking over a part of the baseband processing, the one of the one ormore other wireless base stations 1 is in an overload state and variousadverse effects arise. Therefore, it is considered reasonable toconsider the processing loads of the one or more other wireless basestations 1 in selecting a share destination of baseband processing.

For example, in S105, the first wireless base station 1#1 selects, as ashare destination of baseband processing, one of the one or more otherwireless base stations 1 the number of wireless terminals 2 of which isa predetermined value or less, based on the number of wireless terminals2 managed by each of the one or more other wireless base stations 1 (thesecond wireless base station 1#2 and the third wireless base station1#3).

In S105 of FIG. 4, as an example, assume that the first wireless basestation 1#1 selects the second wireless base station 1#2 as a sharedestination of baseband processing.

Next, in S106 of FIG. 4, the first wireless base station 1#1 selects(determines) a range in which baseband processing of the first wirelessbase station 1#1 is shared with the one (the second wireless basestation 1#2) of the one or more other wireless base stations 1, whichhas been selected in S105. In this case, for example, the range is setin units of the cell 1C.

That is, as illustrated in FIG. 3, the first wireless base station 1#1includes seven RRUs 12, and forms seven cells 1C. In S106, the firstwireless base station 1#1 selects a cell 1C, which is one of the sevencells 1C, the baseband processing of which is shared with the secondwireless base station 1#2. The number of cells 1C to be selected may beone, and may be plural. Also, in selecting a cell 1C the basebandprocessing of which is shared with the second wireless base station 1#2,arbitrary rule and index may be used. For example, in view of themagnitudes of respective processing loads of both of the first wirelessbase station 1#1, which is a share source of baseband processing, andthe second wireless base station 1#2, which is a share destination ofthe baseband processing, the first wireless base station 1#1 may selecta cell 1C the baseband processing of which is shared with the secondwireless base station 1#2.

In S106 of FIG. 4, as an example, assume that the first wireless basestation 1#1 selects, as the range in which the baseband processing ofthe first wireless base station 1#1 is shared with the second wirelessbase station 1#2, the third cell 1C formed by the third RRU 12, which isone of the three cells 1C managed by the first wireless base station 1#1itself.

Next, in S107 of FIG. 4, the first wireless base station 1#1 requeststhe second wireless base station 1#2 to share baseband processing. Thisis realized by transmission of a signal that requests sharing ofbaseband processing to the second wireless base station 1#2, which isperformed by the first wireless base station 1#1. For the sake ofconvenience, the signal is referred to as a sharing request signal.

The sharing request signal may include various types of information(parameters) related to sharing of baseband processing. For example, thesharing request signal may include the identifier of one of the wirelessbase stations 1, which is a share source (a request source), theidentifier of one of the one or more other wireless base stations 1,which is a share destination (a request destination) selected in S105,and the identifier of the cell 1C, which is a share target selected inS106. Also, the sharing request signal may include information, such asa start timing of sharing of baseband processing, the number of wirelessterminals 2 coupled to the cell 1C, which is a share target, and thelike.

In S107 of FIG. 4, the second wireless base station 1#2 receives asharing request signal from the first wireless base station 1#1. Inresponse to the sharing request signal, in S108, the second wirelessbase station 1#2 determines whether or not requested sharing isacceptable. The second wireless base station 1#2 may perform thedetermination using various types of information Included in the sharingrequest signal and other various types of information.

In S109, the second wireless base station 1#2 transmits a responsesignal to the sharing request signal to the first wireless base station1#1. For the sake of convenience, the signal IS referred to as a sharingrequest response signal. A content of the sharing request responsesignal reflects determination of S108. That is, if it is determined inS108 that sharing is acceptable, the sharing request response signalindicates that sharing is acceptable. On the other hand, if it isdetermined in S108 that sharing is not acceptable, the sharing requestresponse signal indicates that sharing is not acceptable.

In FIG. 4, as an example, assume that, in S108, the second wireless basestation 1#2 determines that sharing of baseband processing is acceptableand, in S109, the second wireless base station 1#2 transmits a sharingrequest response signal indicating that sharing is acceptable.

In S109 of FIG. 4, the first wireless base station 1#1 receives thesharing request response signal from the second wireless base station1#2. As described above, the sharing request response signal in FIG. 4indicates that sharing of baseband processing is acceptable. Then, inS110, in response to the sharing request response signal indicating thatsharing of baseband processing is acceptable, the first wireless basestation 1#1 starts sharing of baseband processing.

As described above, in the second embodiment, hierarchical layers thatform a protocol stack of LTE are divided into two, the physical layer ishandled as a hierarchical layer that performs “a process that has a timelimitation”, and the MAC layer and higher layers are handled ashierarchical layers each of which performs “a process that does not havea time limitation”. Thus, in S110, based on the above-describeddivision, sharing of baseband processing between the wireless basestations 1 is performed.

More specifically, in S110, the first wireless base station 1#1, whichis a share source of baseband processing, executes a process, in thebaseband processing, which is performed by the physical layer, byitself. On the other hand, the second wireless base station 1#2, whichis a share destination of the baseband processing, executes (takes over)processes, in the baseband processing, which are performed by the MAClayer and higher layers, instead of the first wireless base station 1#1.In this case, passing of a baseband signal between the physical layerand the MAC layer is performed, and this is realized by transmission andreception of the baseband signal between the first wireless base station1#1 and the second wireless base station 1#2.

In addition, in this case, in S110, a target of execution of theprocesses of the MAC layer and higher layers performed by the secondwireless base station 1#2 is determined based on selection of a sharingrequest target in S106 and the sharing request signal in S107. That is,a target of execution of the processes of the MAC layer and higherlayers performed by the second wireless base station 1#2 is a partrelated to the third cell 1C, among the three cells 1C managed by thefirst wireless base station 1#1, which is formed by the third RRU 12.Also, if the sharing request signal in S107 includes various types ofinformation (parameters) related to sharing of baseband processing, thesharing in S110 is executed based on the various types of information.For example, if the sharing request signal includes informationindicating a start timing of sharing of baseband processing, the sharingin S110 is performed based on the start timing.

Note that, an end of sharing may be determined and executed by anarbitrary method. For example, if the processing load of the firstwireless base station 1#1 is a predetermined value or less, the firstwireless base station 1#1 may request the second wireless base station1#2 to end sharing.

Also, for example, between S109 and S110, the first wireless basestation 1#1 may transmit information that is used by the second wirelessbase station 1#2 in performing a shared part of baseband processing tothe second wireless base station 1#2 (not illustrated in FIG. 4). Forexample, in this embodiment, the second wireless base station 1#2executes the processes of the MAC layer and higher layers, andtherefore, the first wireless base station 1#1 is enabled to transmitvarious types of information (specifically, for example, the identifierof a terminal, and the like) managed by each of the MAC layer and higherlayers to the second wireless base station 1#2. Thus, the secondwireless base station 1#2 is enabled to smoothly perform the shared partof baseband processing.

As described above with reference to FIG. 4, according to the secondembodiment, when baseband processing of one of the wireless basestations 1 is shared with one of the one or more other wireless basestations 1, one of the wireless base stations 1 may perform at least aprocess, in the baseband processing, which has a processing timelimitation (by itself).

Note that, in FIG. 4, each of processes of S101 to S110 performed by thewireless base stations 1 is performed by the corresponding one of theBBUs 11 included in the wireless base stations 1. The configurations ofthe wireless base stations 1 and the BBUs 11 will be described later.

The processing flow illustrated in FIG. 4 has been described so far, andmodified examples will be described below.

As described above, in S103, the first wireless base station 1#1determines, based on information related to the processing load of thefirst wireless base station 1#1 itself, whether or not sharing ofbaseband processing is desired. However, in determining whether or notsharing of baseband processing is desired, an index other thaninformation related to the processing load of the first wireless basestation 1#1 itself may be considered. As an example, considering alsothe processing loads of the one or more other wireless base stations 1,whether or not sharing of baseband processing is desired may bedetermined.

As described above, in S105, the first wireless base station 1#1selects, based on information related to the processing loads of the oneor more other wireless base stations 1, a share destination of basebandprocessing. However, in selecting a share destination of basebandprocessing, an index other than information related to the processingloads of the one or more other wireless base stations 1 may beconsidered.

As such an index, for example, information related to a communicationdelays between the self wireless base station 1 and each of the one ormore other wireless base stations 1 may be used. If one of the one ormore other wireless base stations 1, which causes a great communicationdelay, is selected as a share destination, a baseband signal passingtime is prolonged based on the communication delay. If, although aprocess, in baseband processing, which has a relatively small timelimitation, is shared with the one of the one or more other wirelessbase stations 1, the baseband signal passing time is longer thanexpected, the time limitation is not satisfied, thus resulting in aproblem. Therefore, a share destination of baseband processing isselected, based on information related to communication delay betweenthe self wireless base station 1 and each of the one or more otherwireless base stations 1.

For example, the first wireless base station 1#1 measures a round triptime (RRT) between the first wireless base station 1#1 and each of theone or more other wireless base stations 1 (the second wireless basestation 1#2 and the third wireless base station 1#3), and thus,information related to a communication delay therebetween may beacquired. A distance between the wireless base stations 1 measured by anarbitrary method may be used as information related to a communicationdelay.

The index used in selecting a share destination in S105 is not limitedto the above-described indexes, and an arbitrary index may be used.Needless to say, a single index may be used, and a plurality of indexesmay be used in combination. Also, a share destination may be fixed(targeted) in each of the wireless base stations 1, that is, forexample, the first wireless base station 1#1 may select the secondwireless base station 1#2 each time.

According to the above-described second embodiment, even when basebandprocessing of one of the wireless base stations 1 is shared with one ofthe one or more other wireless base stations 1, the one of the wirelessbase stations 1 performs at least a process, in the baseband processing,which has a processing time limitation (by itself). Thus, the process,in the baseband processing, which has a processing time limitation, isnot influenced by a delay caused by passing of a baseband signal.Therefore, according to the second embodiment, similar to the firstembodiment, the problem of a time limitation for baseband processingbased on the specification of a wireless communication protocol may besolved.

Third Embodiment

A third embodiment will be described with reference to FIG. 5 and FIG.6. In the above-described second embodiment, the wireless base station 1itself determines whether or not sharing of baseband processing isdesired. In contrast, in the third embodiment, a control device 3, whichis different from the wireless base station 1, determines whether or notsharing of baseband processing is desired.

The third embodiment shares many common points with the secondembodiment. Therefore, the third embodiment will be described below withfocus on different points from the second embodiment.

First, a system configuration of a wireless communication systemaccording to the third embodiment will be described with reference toFIG. 5.

In comparison with the system configuration according to the secondembodiment illustrated in FIG. 3, the control device 3 is added in asystem configuration according to the third embodiment illustrated inFIG. 5. The control device 3 may be, for example, the same device as anevolved packet core (EPC) device, a mobility management entity (MME)device, or the like, in an LTE system, and may be a different devicefrom these devices. The control device 3 is coupled to each of thewireless base stations 1 by an optical fiber, or the like, via anoptical switch (not illustrated), and may perform a low-delaycommunication.

Next, a sequence diagram illustrating a processing flow in a wirelesscommunication system according to the third embodiment will be describedwith reference to FIG. 6.

First, in S201 of FIG. 6, similar to S101 of FIG. 4, each of thewireless base stations 1 acquires information (an index) related to theprocessing load of the wireless base station 1 itself.

Next, in S202 of FIG. 6, each of the wireless base stations 1 (the firstwireless base station 1#1 to the third wireless base station 1#3)transmits the information related to the processing load of the wirelessbase station 1 itself acquired in S201 to the control device 3. Thus,the control device 3 acquires information related to the processing loadof each of the wireless base stations 1.

In S203 of FIG. 6, the control device 3 determines whether or notsharing of baseband processing is desired in each of the wireless basestations 1 in a similar manner to that performed by the first wirelessbase station 1#1 in S103 of FIG. 4. In S203, as an example, assume thatthe control device 3 determines whether or not sharing of basebandprocessing is desired in the first wireless base station 1#1.

S204 of FIG. 6 is similar to S104 of FIG. 4.

Next, in S205 of FIG. 6, the control device 3 selects (determines) oneof the one or more other wireless base stations 1, which is to be ashare destination of baseband processing, in a similar manner to thatperformed by the first wireless base station 1#1 in S105 of FIG. 4. InS205, as an example, assume that the control device 3 selects the secondwireless base station 1#2 as a share destination of baseband processingin the first wireless base station 1#1.

In S206 of FIG. 6, the control device 3 selects (determines) a range inwhich baseband processing is shared with one (the second wireless basestation 1#2) of the one or more wireless base stations 1 in a similarmanner to that performed by the first wireless base station 1#1 In S106of FIG. 4. In S206, as an example, assume that the control device 3selects, as the range in which baseband processing is shared with thesecond wireless base station 1#2, the third cell 1C formed by the thirdRRU 12, among the three cells 1C managed by the first wireless basestation 1#1.

In S207 of FIG. 6, based on S203 to S206, the control device 3 requests(Instructs) the first wireless base station 1#1, which is a share sourceof baseband processing, and the second wireless base station 1#2, whichis a share destination of the baseband processing, to share the basebandprocessing.

In S208 of FIG. 6, the first wireless base station 1#1 and the secondwireless base station 1#2 start sharing of the baseband processing in asimilar manner to that performed in S110 of FIG. 4.

The processing flow illustrated in FIG. 6 has been described so far.Note that, in S206 of FIG. 6, the control device 3 unilaterallyinstructs each of the wireless base stations 1 to share basebandprocessing. However, the wireless base stations 1 that are a sharesource and a share destination of baseband processing may refuse sharingrequested (Instructed) by the control device 3.

According to the third embodiment, which has been described above, evenwhen baseband processing of one of the wireless base stations 1 isshared with the one or more wireless base stations 1, the one of thewireless base stations 1 performs at least a process, in the basebandprocessing, which has a processing time limitation (by itself). Thus,the process, in the baseband processing, which has a time limitation, isnot influenced by a delay caused by passing of a baseband signal.Therefore, according to the third embodiment, similar to each of theabove-described embodiments, the problem of a time limitation forbaseband processing based on the specification of a wirelesscommunication protocol may be solved.

Modified Examples and the Like

Modified examples of the above-described embodiments will be describedbelow. Each of the following modified examples may be combined with eachof the above-described embodiments independently or in combination withanother one of the modified examples.

First, in the above-described second embodiment and the like, indivision of baseband processing, a process of a physical layer in aprotocol stack of an LTE system is handled as “a process that has a timelimitation”, and processes of the MAC layer and higher layers thereinare handled as “processes that do not have a time limitation”. However,the above-described division is merely an example, and basebandprocessing may be divided at a different boundary. As an example, theprocesses of the MAC layer and lower layers may be handled as “processesthat have a time limitation”, and processes of the RLC layer and higherlayers may be handled as “processes that do not have a time limitation”.

Division of baseband processing into “a process that has a timelimitation” and “a process that does not have a time limitation” may beperformed in view different from protocol stack hierarchical layers. Forexample, a process for which a time limitation defined in the (standard)specification is a predetermined time or more may be handled as “aprocess that has a time limitation”, and a process that is not theabove-described process may be handled as “a process that does not havea time limitation”.

Furthermore, in each of the above-described embodiments, basebandprocessing is divided into two types, that is, “a process that has atime limitation” and “a process that does not have a time limitation”,and the baseband processing is shared with two wireless base stations 1(the BBUs 11), based on the division. However, baseband processing maybe divided into three or more types, and the baseband processing may beshared with three or more wireless base stations 1 (the BBUs 11), basedon the division. For example, baseband processing may be divided intothree, that is, “a process that has a relatively large time limitation”,“a process that has an intermediate level time limitation”, and “aprocess that has a relatively small time limitation”, and three wirelessbase stations 1 (the BBUs 11) may share the baseband processing, basedon the division.

In the above-described second embodiment and the like, a range ofsharing of baseband processing is selected in units of the cell 1C.However, this is merely an example, and the range of sharing of basebandprocessing may be selected in some other unit. For example, the range ofsharing of baseband processing may be selected in units of a sector,which forms the cell 1C.

Functional Configuration of Each Device in Wireless Communication SystemAccording to Each Embodiment

Next, functional configurations of the wireless base station 1 and thecontrol device 3 in a wireless communication system according to each ofthe above-described embodiments will be described with reference to FIG.7 and FIG. 8.

FIG. 7 is a block diagram illustrating an example of a functionalconfiguration of the wireless base station 1 (the first wireless basestation 1#1 to the third wireless base station 1#3 In each embodiment).As illustrated in FIG. 7, for example, the wireless base station 1 isdivided into one BBU 11 and one or more RRUs 12. The BBU 11 includes acontrol section 111, a storage section 112, and a communication section113. Also, each of the RRUs 12 includes a communication section 121 anda wireless communication section 122.

The control section 111 of the BBU 11 performs control of various typesof processing related to wireless communication performed by thewireless base station 1 with a wireless terminal 2. Processingcontrolled by the control section 111 includes every processing executedby each of the wireless base stations 1, whether or not there is cleardescription thereof in each of the above-described embodiments andmodified examples.

The storage section 112 of the BBU 11 stores various types ofinformation related to wireless communication performed by the wirelessbase station 1 with the wireless terminal 2. Information stored in thestorage section 112 includes every information handled by each of thewireless base stations 1, whether or not there is clear descriptionthereof in each of the above-described embodiments and modifiedexamples.

The communication section 113 of the BBU 11 transmits and receivesvarious signals related to wireless communication performed by thewireless base station 1 with the wireless terminal 2 to and from eachdevice. Devices to and from which the communication section 113transmits and receives signals include the RRUs 12 under controlperformed by the communication section 113 itself, the one or more otherwireless base stations 1 (the BBUs 11 or the RRUs 12), the controldevice 3, and the like. Signals transmitted and received by thecommunication section 113 include every signal transmitted and receivedby each of the wireless base stations 1 or the BBU 1 to and from theRRUs 12 under control performed by the communication section 113 itself,the one or more other wireless base stations 1 (the BBUs 11 or the RRUs12), the control device 3, and the like, whether or not there is cleardescription thereof in each of the above-described embodiments andmodified examples.

The communication section 121 of each of the RRUs 12 transmits andreceives various signals related to wireless communication performed bythe wireless base station 1 with the wireless terminal 2 to and fromeach device. Devices to and from which the communication section 121transmits and receives signals include the BBU 11 that manages thecommunication section 121, the one or more other wireless base stations1 (the BBUs 11), and the like. Signals transmitted and received by thecommunication section 121 include every signal transmitted and receivedby each of the wireless base stations 1 or the RRUs 12 to and from theBBU 11 that manages the communication section 121, the one or more otherwireless base stations 1 (the BBUs 11), and the like, whether or notthere is clear description thereof in each of the above-describedembodiments and modified examples.

The wireless communication section 122 of each of the RRUs 12 transmitsand receives various wireless signals related to wireless communicationperformed by the wireless base station 1 with the wireless terminal 2 toand from the wireless terminal 2 and the like. Wireless signalstransmitted and received by the wireless communication section 122include every wireless signal transmitted and received by each of thewireless base stations 1 or the RRUs 12 to and from the wirelessterminal 2 and the like, whether or not there is clear descriptionthereof in each of the above-described embodiments and modifiedexamples.

FIG. 8 is a block diagram illustrating an example of a functionalconfiguration of the control device 3 in the third embodiment. Asillustrated in FIG. 8, the control device 3 includes a control section31, a storage section 32, and a communication section 33.

The control section 31 of the control device 3 performs control ofvarious types of processing related to wireless communication performedby the wireless base station 1 with the wireless terminal 2. Processingcontrolled by the control section 31 includes every processing executedby the control device 3, whether or not there is clear descriptionthereof in each of the above-described embodiments and modifiedexamples.

The storage section 32 of the control device 3 stores various types ofinformation related to wireless communication performed by the wirelessbase station 1 with the wireless terminal 2. Information stored in thestorage section 32 includes every information handled by the controldevice 3, whether or not there is clear description thereof in each ofthe above-described embodiments and modified examples.

The communication section 33 of the control device 3 transmits andreceives various signals related to wireless communication performed bythe wireless base station 1 with the wireless terminal 2 to and fromeach device. Devices to and from which the communication section 33transmits and receives signals include each of the wireless basestations 1 (the BBUs 11), and the like. Signals transmitted and receivedby the communication section 33 include every signal transmitted andreceived by the control device 3 to and from each of the wireless basestations 1 (the BBUs 11), and the like, whether or not there is cleardescription thereof in each of the above-described embodiments andmodified examples.

Hardware Configuration of Each Device in Wireless Communication SystemAccording to Each Embodiment

Hardware configurations of the wireless base station 1 and the controldevice 3 in a wireless communication system according to each embodimentand each modified example will be described with reference to FIG. 9 andFIG. 10.

FIG. 9 is a diagram illustrating a hardware configuration of thewireless base station 1 (the first wireless base station 1#1 to thethird wireless base station 1#3 in each embodiment). As illustrated inFIG. 9, for example, the wireless base station 1 is divided into one BBU11 and one or more RRUs 12. The BBU 11 includes a processor 1101, amemory 1102, and a communication interface (IF) 1103. Also, each of theRRUs 12 includes a communication IF 1201, an RF circuit 1202, and anantenna 1203.

The processor 1101 is, for example, a central processing unit (CPU) or adigital signal processor (DSP). The processor 1101 may be realized by adigital electronic circuit herein. Examples of the digital electroniccircuit include a field-programmable gate array (FPGA), an applicationspecific integrated circuit (ASIC), a large scale integration (LSI), andthe like.

The memory 1102 includes, for example, at least one of a random accessmemory (RAM), such as a synchronous dynamic random access memory (SDRAM)and the like, a read only memory (ROM), and a flash memory, and stores aprogram, control information, and data. In addition to theabove-described components, the wireless base station 1 may include anauxiliary storage device (a hard disk, or the like), which is notillustrated, and the like. Each of the communication IF 1103 and thecommunication IF 1201 is, for example, a communication interfacerealized by an optical fiber.

Correspondence between the functional configuration of the wireless basestation 1 illustrated in FIG. 7 and the hardware configuration of thewireless base station 1 illustrated in FIG. 9 will be described. Thecontrol section 111 is realized by, for example, the processor 1101, thememory 1102, and a digital electronic circuit (not illustrated), and thelike. The storage section 112 is realized by, for example, the memory1102. The communication section 113 is realized by, for example, thecommunication IF 1103. The communication section 121 is realized by, forexample, the communication IF 1201. The wireless communication section122 is realized by, for example, the RF circuit 1202 and the antenna1203.

FIG. 10 is a diagram illustrating an example of a hardware configurationof the control device 3. As illustrated in FIG. 10, the control device 3includes a processor 301, a memory 302, and a communication interface(IF) 303.

The processor 301 is, for example, a central processing unit (CPU) or adigital signal processor (DSP). The processor 301 may be realized by adigital electronic circuit herein. Examples of the digital electroniccircuit include a field-programmable gate array (FPGA), an applicationspecific integrated circuit (ASIC), a large scale integration (LSI), andthe like.

The memory 302 includes, for example, at least one of a random accessmemory (RAM), such as a synchronous dynamic random access memory (SDRAM)and the like, a read only memory (ROM), and a flash memory, and stores aprogram, control information, and data. In addition to theabove-described components, the wireless base station 1 may include anauxiliary storage device (a hard disk, or the like), which is notillustrated, and the like. The communication IF 303 is, for example, acommunication interface realized by an optical fiber.

Correspondence between the functional configuration of the controldevice 3 illustrated in FIG. 8 and the hardware configuration of thecontrol device 3 illustrated in FIG. 10 will be described. The controlsection 31 is realized by, for example, the processor 301, the memory302, and a digital electronic circuit (not illustrated), and the like.The storage section 32 is realized by, for example, the memory 302. Thecommunication section 33 is realized by, for example, the communicationIF 303.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the inventionand the concepts contributed by the inventor to furthering the art, andare to be construed as being without limitation to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority andinferiority of the invention. Although the embodiments of the presentinvention have been described in detail, it should be understood thatthe various changes, substitutions, and alterations could be made heretowithout departing from the spirit and scope of the invention.

What is claimed is:
 1. A wireless communication system comprising: awireless terminal; and a wireless base station configured to: perform awireless communication with the wireless terminal, perform a portion ofbaseband processing procedure for the wireless communication, whereinthe baseband processing procedure being shared between the wireless basestation and a second wireless base station, wherein the portion of thebaseband processing procedure performed by the wireless base stationcomprises a processing procedure that has a limitation on a processingtime, wherein the limitation requires the processing by the wirelessbase station to be completed within a specific period of time; andwherein the second wireless base station being configured to perform aremaining portion of the baseband processing procedure other than theportion of the baseband processing procedure performed by the wirelessbase station.
 2. The wireless communication system according to claim 1,wherein the portion of the baseband processing procedure performed bythe wireless base station is a processing performed in at least oneprotocol layer lower than a given protocol layer of a wirelesscommunication protocol used for the wireless communication.
 3. Thewireless communication system according to claim 1, wherein the portionof the baseband processing procedure performed by the wireless basestation is a processing performed in a physical layer of a wirelesscommunication protocol used for the wireless communication.
 4. Thewireless communication system according to claim 1, wherein the secondwireless base station is configured to perform the remaining portion ofthe baseband processing procedure the remaining portion of the basebandprocessing procedure being a processing that does not have thelimitation on the processing time.
 5. The wireless communication systemaccording to claim 1, wherein the wireless base station is configured todetermine when to share the baseband processing procedure between thewireless base station and the second wireless base station.
 6. Thewireless communication system according to claim 1, further comprising:a control device configured to determine when to share the basebandprocessing procedure between the wireless base station and the differentwireless base station.
 7. The wireless communication system according toclaim 1, wherein the wireless base station includes a baseband unit anda plurality of radio frequency units coupled to the baseband unit, eachof the plurality of radio frequency units forming each of a plurality ofcells.
 8. The wireless communication system according to claim 7,wherein the sharing of the baseband processing procedure is performed inunits of the plurality of cells.
 9. The wireless communication systemaccording to claim 1, wherein the second wireless base station isselected from among a plurality of other wireless base stations based oneach load of each of the plurality of other wireless base stations. 10.The wireless communication system according to claim 1, wherein thesecond wireless base station is selected from among a plurality of otherwireless base stations based on each communication delay between thewireless base station and each of the plurality of other wireless basestations.
 11. A wireless base station comprising: a memory; and aprocessor coupled to the memory and configured to: perform a wirelesscommunication with a wireless terminal, perform a portion of basebandprocessing procedure for the wireless communication, wherein thebaseband processing procedure being shared between the wireless basestation and a second wireless base station, wherein the portion of thebaseband processing procedure performed by the wireless base stationcomprises a processing procedure that has a limitation on a processingtime wherein the limitation requires the processing by the wireless basestation to be completed within a specific period of time; and whereinthe second wireless base station being configured to perform a remainingportion of the baseband processing procedure other than the portion ofthe baseband processing procedure performed by the wireless basestation.
 12. A wireless base station comprising: a memory; and aprocessor coupled to the memory and configured to: receive a requestsignal requesting to share a baseband processing procedure between thewireless base station and a second wireless base station, the basebandprocessing procedure being for a wireless communication between thesecond wireless base station and a wireless terminal, and perform aportion of the baseband processing procedure for the wirelesscommunication, wherein the portion of the baseband processing procedureperform by the wireless base station comprises a processing procedurethat does not have a limitation on a processing time, and wherein thesecond wireless base station being configured to perform a remainingportion of the baseband processing procedure other than the portion ofthe baseband processing procedure performed by the wireless basestation.